The endless belts used for moderate load power transmission applications in automobiles, which are more commonly collectively termed fan belts, are constructed of a flexible, tear-resistant polymeric material and are manufactured in countless different sizes to accommodate the varying pulley sizes and spacings therebetween found in the vast number of different models of automobiles sold and driven in the United States and foreign countries. While these endless belts are quite durable, they nevertheless are subjected to a great deal of stress due to their high speed operation and consequently must be periodically replaced. Thus, for a garage to be able to meet the needs of its customers, it is necessary to stock a large number of differently sized belts. This presents a substantial inventory problem to the garage as these belts are of a fixed size and consequently a belt suitable for one make of automobile cannot generally be used in another.
In addition to having to stock a large inventory of these belts, a garage mechanic must often expend a good deal of labor in securing the belt about the pulleys due to the limited flexibility inherent in such belts and the often encountered awkward positioning of the pulleys with respect to the automobile body presenting the mechanic with restricted access for mounting the belt on the pulleys.
The problems of fixed belt size and installation could be greatly relieved if the belt were either adjustable or of a construction whereby it could be readily assembled on site to the desired size for a particular application, e.g., in an auto repair garage by an auto repair person for a particular model of automobile. One solution to the problems of fixed belt size and installation is found in applicant's U.S. Pat. No. 4,031,766 wherein an adjustable belt is provided which can be assembled about the pulleys and thereby facilitate installation while obviating the need for an inventory of differently sized belts. That solution employs a belt having a male end of reduced diameter and a female end having a channel therein equal in length to the reduced diameter portion of the male end. To define a belt having the desired size, equal precalculated lengths are severed from both the male and female ends, and an adhesive is applied about the male end which is then inserted into the female end of the belt. To avoid any gaps which would otherwise weaken and imbalance the belt, these cuttings have to be carefully made to insure that the length of the reduced diameter portion of the male end is equal to the length of the channel in the female end.
An improvement to the above-described patented belt configuration is disclosed in applicant's U.S. Pat. No. Re. 33,389. In the improved structure, an outer length of flexible and durable belt material is provided with a centrally disposed channel extending therethrough and a flexible and durable cord is slidably disposed within the channel and extends the length thereof. An endless belt of the desired size is formed by cutting the length of belt material with the reinforcing cord contained therein to the desired length, pulling a portion of the cord from one end of the outer length of belt material and applying an adhesive to the exposed cord and the ends of the belt material. The exposed portion of the reinforcing cord is then inserted into the open channel in the other end of the outer length of belt material until the ends of the outer length of material are in an abutting relationship. As the reinforcing cord is of the same length as the outer length of material, the ends of the reinforcing cord will also be in an abutting relationship within the outer length of material. Upon setting of the adhesive, a durable endless belt of the desired size is formed. While such a belt construction and forming process retains the ease of installation and adjustability of the earlier patented construction, it eliminated the need for having to make to precise cuts during the belt forming process and provides the resultant belt with superior strength characteristics. However, it has been found that such a construction is relatively expensive due to the costs of forming a cylindrical longitudinal channel in the outer belt length.
A further improvement to the above-described belts and their methods of manufacture is found applicant's copending application Ser. No. 08/574,845. The further improved configuration comprises an outer length of flexible, tear-resistant material defining parallel inner and outer surfaces formed into a closed loop of desired size. The outer length of material has a generally rectangular interior channel therein extending about the loop proximate the inner surface thereof. A reinforcing ribbon of tear-resistant, flexible material is disposed within the channel and extends about the loop, traversing the abutting ends of the outer length of material and overlapping itself within the interior channel. An adhesive is provided within the interior channel for securing the reinforcing ribbon therein to the interior of the outer length of material and for securing together the overlapping portions of the reinforcing ribbon within the channel thereby providing a strong and durable transmission belt.
The aforesaid endless belt was adapted to be formed on site into any desired length either manually or automatically with a belt forming apparatus. This was achieved by providing the outer length of belt material with a longitudinally extending radial slit in the outer surface of the length of belt material which communicated with the interiorly disposed channel. The outer length of belt material was first cut to the desired length such that the extended ends thereof defined acutely angled mating surfaces. In the preferred process for forming the belt, the adhesive and reinforcing ribbon were concurrently fed into the interior channel in the outer length of belt material through the radial slit therein as the outer length of belt material was formed into a closed loop. The ribbon and adhesive continued to be fed into the channel after the leading end of the outer length of belt material was brought into abutment with the trailing end to form the endless loop such that the reinforcing ribbon and adhesive extended across the abutting ends of the outer length of belt material and about the loop defined thereby as above described. The ribbon was then severed such that a short length thereof projected radially from the interior channel through the slit in the belt material. The protruding ribbon was then pressed into the channel through the slit over the previously inserted adhesive and ribbon. The abutting ends of outer length of belt material were then clamped together in a mating relationship as the adhesive quickly set, completing the belt forming process.
This embodiment of the belt and method of construction retained the strength characteristics of the previously discussed earlier embodiments and significantly reduced the cost of construction. However, in many of these belts, particularly in the longer sizes, work hardening was found in the cured adhesive. Because the adhesive layers within the belt were relatively thin, such a condition could lead to failure after extended periods of use. The work hardening of the adhesive was found to have resulted from high frequency vibration in the belt during use. The vibration was found to be caused by a combination of natural resonance during high speed use, the higher coefficient of friction exhibited by the polyurethane belt material and slight imbalances in the belts.
Some natural vibration in the belt during high speed use is unavoidable. The higher coefficient of friction in the belt material caused the belt to tend to "hug" the pulley during use as opposed to extending tangentially therefrom as occurs with conventional neoprene belts. As a result the belt came off the pulley at outwardly inclined angles which caused the belt to vibrate. This higher coefficient of friction, however, also allowed the belt to be more loosely secured about the pulleys than conventional neoprene belts, reducing the radial forces exerted on the shafts and thus prolonging the life of the bearings and associated motors such as the water pump. Thus, the potential benefits resulting from use of the polyurethane material weighed against the use of neoprene or other material having a lower coefficient of friction in an effort to solve the vibration problem. The slight imbalance in these belts, which also contributed to the vibration, was caused in part by the overlapping portion of the ribbon within the belt and, in part, by non-uniformities in the extruded outer length of belt material. The overlap of the reinforcing ribbon within the outer length of belt material was deemed necessary due to the difficulties encountered in securely adhering the ribbon to the polyurethane. The ribbon to ribbon securement was considerably stronger.
The endless belts and forming processes disclosed herein retain all of the advantages of the above-discussed prior embodiments while substantially diminishing the deleterious effects of work hardening in the cured adhesive, thereby significantly improving the useful life of the belt.